Perpendicular magnetic recording medium and method of manufacturing perpendicular magnetic recording medium

ABSTRACT

A perpendicular magnetic recording medium  100  having a magnetic recording layer  122 , wherein a particle diameter of crystal grains in layer  122  improves a SNR while a high coercive force is maintained. There also is at least a ground layer  118 , a first magnetic recording layer  122   a , and a second magnetic recording layer  122   b  in this order on a disk base  110 . The first layer  122   a  and the second layer  122   b  are ferromagnetic layers, each having a granular structure in which a grain boundary part made of a non-magnetic substance is formed between crystal grains each grown in a columnar shape, and A&lt;B when an average particle diameter of the crystal grains in the first magnetic recording layer  122   a  is taken as A nm and an average particle diameter of the crystal grains in the second magnetic recording layer  122   b  is taken as B nm.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.12/934,935 filed Dec. 27, 2010 claiming priority based on InternationalApplication No. PCT/JP2009/056050 filed Mar. 26, 2009, claiming prioritybased on Japanese Patent Application No. 2008-082250, filed on Mar. 26,2008, the disclosures of which are incorporated herein by reference intheir entirety.

TECHNICAL FIELD

The present invention relates to a perpendicular magnetic recordingmedium implemented on an HDD (hard disk drive) of a perpendicularmagnetic recording type or the like, and a method of manufacturing aperpendicular magnetic recording medium.

BACKGROUND ART

With an increase in capacity of information processing in recent years,various information recording technologies have been developed. Inparticular, the surface recording density of an HDD using magneticrecording technology is continuously increasing at an annual rate ofapproximately 100%. In recent years, an information recording capacityexceeding 160 GB per one magnetic disk with a 2.5-inch diameter for usein an HDD or the like has been desired. To fulfill such demands, aninformation recording density exceeding 250 Gbits per one square inch isdesired to be achieved.

To attain a high recording density in a magnetic disk for use in an HDDor the like, a magnetic disk of a perpendicular magnetic recording typehas been suggested in recent years. In a conventional in-plane magneticrecording type, the axis of easy magnetization of a magnetic recordinglayer is oriented in a plane direction of a base surface. In theperpendicular magnetic recording type, by contrast, the axis of easymagnetization is adjusted so as to be oriented in a directionperpendicular to the base surface.

For example, Patent Document 1 discloses a technology regarding aperpendicular magnetic recording medium configured to have a groundlayer, a Co-type perpendicular magnetic recording layer, and aprotective layer in this order formed on a substrate. Also, PatentDocument 2 discloses a perpendicular magnetic recording medium having astructure attached with an artificial lattice film continuous layer(exchange coupling layer) exchange-coupled to a particulate recordinglayer.

In the perpendicular magnetic recording type, compared with the in-planerecording type, a thermal fluctuation phenomenon can be suppressed, andtherefore the perpendicular magnetic recording type is suitable forincreasing the recording density.

Also, conventionally, for the purpose of improving a coercive force Hcand a Signal-Noise Ratio (SNR), a structure in which a magneticrecording layer is formed of two layers has been suggested. For example,Patent Document 3 discloses a configuration in which, with a magneticrecording layer being formed of two layers, one recording layer on abase side has a composition containing CoCrPtTa and the other recordinglayer on a side away from the side has a composition containing CoCrPtB.

-   Patent Document 1: Japanese Unexamined Patent Application    Publication No. 2002-92865-   Patent Document 2: U.S. Pat. No. 6,468,670-   Patent Document 3: Japanese Unexamined Patent Application    Publication No. 2001-256632

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

As described above, for achieving a higher recording density, thecoercive force Hc is required to be improved. To improve the coerciveforce Hc, a method of making the film thickness of the magneticrecording layer thicker can be thought. When the film thickness is madethicker, however, the SNR is decreased.

To get around this, the inventors of the present application found thatthe magnetic recording layer is configured to have a two-layer structureand the amount of a non-magnetic substance forming a grain boundary ofthe two-layer magnetic recording layer (the ratio with respect to amagnetic substance) is appropriately controlled, thereby improving theSNR while improving the coercive force Hc.

However, as a result of detailed studies about the magnetic recordinglayer of a two-layer structure, the inventors of the present applicationfound that the coercive force Hc and the SNR are not necessarilydetermined only by the composition or amount of the non-magneticsubstance. That is, it was found that, even if the composition (materialand ratio) of the crystal grains formed of a magnetic substance and thatof the grain particle formed of a non-magnetic substance are the same,the SNR varies based on another factor.

The present invention has been devised in view of the above problem ofthe magnetic recording layer. An object of the present invention is toprovide a perpendicular magnetic recording medium including a magneticrecording layer, the medium in which a particle diameter of crystalgrains in the magnetic recording layer of a two-layer structure is sodesigned as to improve an SNR while a high coercive force is maintained,and a method of manufacturing a perpendicular magnetic recording medium.

Means for Solving the Problem

To solve the above problem, as a result of diligent studies by theinventors of the present invention, it was found that, with the particlediameters of crystal grains for each layer in a magnetic recording layerformed with two layers having a predetermined relation, the SNR canfurther be improved, thereby completing the present invention.

That is, to solve the above problem, in a typical structure of aperpendicular magnetic recording medium according to the presentinvention, the perpendicular magnetic recording medium includes at leasta ground layer, a first magnetic recording layer, and a second magneticrecording layer in this order on a base, wherein the first magneticrecording layer and the second magnetic recording layer areferromagnetic layers of a granular structure in which grain boundaryparts made of a non-magnetic substance are each formed between crystalgrains each grown in a columnar shape, and A<B when an average particlediameter of the crystal grains in the first magnetic recording layer istaken as A nm and an average particle diameter of the crystal grains inthe second magnetic recording layer is taken as B nm.

With the particle diameter of the crystal grains of the first magneticrecording layer being smaller than the particle diameter of the crystalgrains of the second magnetic recording layer, the crystal grains can bemade finer in the first magnetic recording layer, and the orientation ofthe crystal grains can be improved in the second magnetic recordinglayer. Making the crystal grains finer and improving the orientationhave a trade-off relation. Therefore, with the above structure, themagnetic recording layers can play the respective roles, and it is thuspossible to improve the SNR while maintaining a high coercive force Hc.

A ratio between the average particle diameter of the crystal grains inthe first magnetic recording layer and the average particle diameter ofthe crystal grains in the second magnetic recording layer is preferably0.8<A/B<1.

With this, the SNR can be optimally improved. Note that, when the ratiobetween the average particle diameter of the crystal grains in the firstmagnetic recording layer and the average particle diameter of thecrystal grains in the second magnetic recording layer is not within theabove range, a role of making each magnetic recording layer finer and arole of improving orientation cannot be shared, and therefore animprovement of the SNR cannot be expected even if two magnetic recordinglayers are provided.

A total thickness of the first magnetic recording layer and the secondmagnetic recording layer is preferably equal to or smaller than 15 nm.

The film thickness of the first magnetic recording layer is preferablyequal to or smaller than 5 nm and, desirably 3 nm to 4 nm. This isbecause, if the thickness is smaller than 3 nm, composition separationof the second magnetic recording layer cannot be promoted and, if thethickness is larger than 4 nm, a R/W characteristic (read/writecharacteristic) is degraded. The film thickness of the second magneticrecording layer is preferably equal to or larger than 5 nm and,desirably 7 nm to 15 nm. This is because a sufficient coercive forcecannot be obtained if the film thickness is smaller than 7 nm and a highinverted-magnetic-domain nucleation magnetic field Hn (with a largeabsolute value) cannot be obtained if the film thickness is larger than15 nm.

The non-magnetic substance may include any of chrome, oxygen, or anoxide, or a plurality thereof.

The non-magnetic substance is a substance in which a grain boundary partcan be formed around magnetic particles so that an exchange interactionoperation between crystal grains (magnetic particles or magnetic grains)is suppressed or interrupted, and can be any as long as it is anon-magnetic substance that cannot be incorporated into cobalt (Co).Examples can include chrome (Cr), oxygen (O), and oxides, such assilicon oxide (SiO₂), chrome oxide (Cr₂O₃), titanium oxide (TiO₂),zircon oxide (ZrO₂), tantalum oxide (Ta₂O₅), niobium oxide (Nb₂O₅), andboron oxide (B₂O₃).

The oxide preferably includes one or a plurality of oxides selected fromthe group of SiO₂, TiO₂, Cr₂O₃, Ta₂O₅, Nb₂O₅, B₂O₃, and ZrO₂. Inparticular, SiO₂ has an effect of promoting finer and more isolated(separated from an adjacent magnetic grain) magnetic grains, and TiO₂has an effect of suppressing dispersion in particle diameter of thecrystal grains. Also, Cr₂O₃ can increase the coercive force Hc.Furthermore, by combining these oxides for segregation over the grainboundaries of the magnetic recording layer, both of the advantages canbe enjoyed.

The non-magnetic substance included in the second magnetic recordinglayer preferably includes one or a plurality of oxides selected from thegroup of SiO₂, TiO₂, Cr₂O₃, Ta₂O₅, Nb₂O₅, B₂O₃, and ZrO₂. With this, thegrain boundary parts can be reliably formed, and the crystal grains canbe clearly separated. Therefore, the SNR can be improved.

To solve the above problem, in a typical structure of a method ofmanufacturing a perpendicular magnetic recording medium according to thepresent invention, the perpendicular magnetic recording medium includesat least a ground layer, a first magnetic recording layer, and a secondmagnetic recording layer in this order on a base, wherein, as the firstmagnetic recording layer, a magnetic target is used that includes, in acomposition, any of chrome, oxygen, or an oxide, or a plurality ofoxides, and a gas pressure of approximately 0.5 Pa and a power ofapproximately 100 to approximately 700 W are set, thereby forming aferromagnetic layer of a granular structure in which non-magnetic grainboundary parts are formed each between crystal grains each grown in acolumnar shape, a magnetic target is used that includes, in acomposition, any of chrome, oxygen, or an oxide, or a plurality ofoxides, and a gas pressure of approximately 0.5 Pa and a power ofapproximately 100 to approximately 1000 W are set, thereby forming, asthe second magnetic recording layer, a ferromagnetic layer of a granularstructure in which non-magnetic grain boundary parts are formed eachbetween crystal grains each grown in a columnar shape, and A<B when anaverage particle diameter of the crystal grains in the first magneticrecording layer is taken as A nm and an average particle diameter of thecrystal grains in the second magnetic recording layer is taken as B nm.

Components and description thereof based on a technical idea of theperpendicular magnetic recording medium described above and theirdescription are also applicable to a method of manufacturing theperpendicular magnetic recording medium.

Effect of the Invention

In the perpendicular magnetic recording medium according to the presentinvention, it is possible to include a magnetic recording layer in whicha particle diameter of crystal grains in the magnetic recording layer ofa two-layer structure is so designed as to improve an SNR while a highcoercive force is maintained.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 A diagram for describing the structure of a perpendicularmagnetic recording medium according to an embodiment.

FIG. 2 A descriptive diagram for describing a relation between gaspressure and SNR and a relation between input power and SNRcharacteristic at the time of film-forming a magnetic recording layer.

FIG. 3 A descriptive diagram for describing a relation between anaverage particle diameter of magnetic particles of a first magneticrecording layer and an average particle diameter of magnetic particlesof a second magnetic recording layer and an SNR relation therebetween.

FIG. 4 A descriptive diagram for describing a perpendicular magneticrecording medium manufactured by using a method of manufacturing aperpendicular magnetic recording medium according to an embodiment.

DESCRIPTION OF REFERENCE NUMERALS

-   -   100 . . . perpendicular magnetic recording medium    -   110 . . . disk base    -   112 . . . adhesion layer    -   114 . . . soft magnetic layer    -   114 a . . . first soft magnetic layer    -   114 b . . . spacer layer    -   114 c . . . second soft magnetic layer    -   116 . . . preliminary ground layer    -   118 . . . ground layer    -   118 a . . . first ground layer    -   118 b . . . second ground layer    -   120 . . . non-magnetic granular layer    -   122 . . . magnetic recording layer    -   122 a . . . first magnetic recording layer    -   122 b . . . second magnetic recording layer    -   124 . . . continuous layer    -   126 . . . medium protective layer    -   128 . . . lubricating layer

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, with reference to the attached drawings, preferredembodiments of the present invention are described in detail. Thedimensions, materials, and others such as specific numerical valuesshown in these embodiments are merely examples so as to facilitateunderstanding of the invention, and are not meant to restrict thepresent invention unless otherwise specified. Note that, in thespecification and drawings, components having substantially the samefunctions and structures are provided with the same reference charactersand are not redundantly described, and components not directly relatingto the present invention are not shown in the drawings.

EMBODIMENTS

An embodiment of the method of manufacturing a perpendicular magneticrecording medium according to the present invention is described. FIG. 1is a diagram for describing the structure of a perpendicular magneticrecording medium 100 according to the present embodiment. Theperpendicular magnetic recording medium 100 depicted in FIG. 1 isconfigured of a disk base 110, an adhesion layer 112, a first softmagnetic layer 114 a, a spacer layer 114 b, a second soft magnetic layer114 c, a preliminary ground layer 116, a first ground layer 118 a, asecond ground layer 118 b, a non-magnetic granular layer 120, a firstmagnetic recording layer 122 a, a second magnetic recording layer 122 b,a continuous layer 124, a medium protective layer 126, and a lubricatinglayer 128. Note that the first soft magnetic layer 114 a, the spacerlayer 114 b, and the second soft magnetic layer 114 together form a softmagnetic layer 114. The first ground layer 118 a and the second groundlayer 118 b together form a ground layer 118. The first magneticrecording layer 122 a and the second magnetic recording layer 122 btogether form a magnetic recording layer 122.

As described below, in the perpendicular magnetic recording medium 100shown in the present embodiment, either or both of the first magneticrecording layer 122 a and the second magnetic recording layer 122 b ofthe magnetic recording layer 122 contain oxides of a plurality of types(hereinafter referred to as a “composite oxide”), thereby causingsegregation of the composite oxide in a non-magnetic grain boundary.

For the disk base 110, a glass disk molded in a disk shape bydirect-pressing amorphous aluminosilicate glass can be used. Note thatthe type, size, thickness, and others of the glass disk are notparticularly restricted. A material of the glass disk can be, forexample, aluminosilicate glass, soda lime glass, soda alumino silicateglass, aluminoborosilicate glass, borosilicate glass, quartz glass,chain silicate glass, or glass ceramic, such as crystallized glass. Thisglass disk is sequentially subjected to grinding, polishing, andchemical strengthening, thereby allowing the smooth, non-magnetic diskbase 110 made of chemically-strengthened glass disk to be obtained.

On the disk base 110, the adhesion layer 112 to the continuous layer 124are sequentially formed by DC magnetron sputtering, and the mediumprotective layer 126 can be formed by CVD. Then, the lubricating layer128 can be formed by dip coating. Note that, in view of highproductivity, using an in-line-type film forming method is alsopreferable. In the following, the structure of each layer and itsmanufacturing method are described.

The adhesion layer 112 is an amorphous ground layer formed in contactwith the disk base 110, and includes a function of increasing a peelstrength between the soft magnetic layer 114 formed thereon and the diskbase 110. When the disk base 110 is made of amorphous glass, theadhesion layer 112 is preferably an amorphous alloy film so as to complywith that amorphous glass surface.

As the adhesion layer 112, for example, a CrTi-type amorphous layer canbe selected.

The soft magnetic layer 114 is a layer in which a magnetic path istemporarily formed at the time of recording so as to let a magnetic fluxpass through a recording layer in a perpendicular direction in aperpendicular magnetic recording type. By interposing the non-magneticspacer layer 114 b between the first soft magnetic layer 114 a and thesecond soft magnetic layer 114 c, the soft magnetic layer 114 can beconfigured to include Antiferro-magnetic exchange coupling (AFC). Withthis, magnetizing directions of the soft magnetic layer 114 can bealigned with high accuracy along the magnetic path (magnetic circuit),the number of perpendicular components in the magnetizing directionbecomes extremely small, and therefore noise occurring from the softmagnetic layer 114 can be reduced. As the composition of the first softmagnetic layer 114 a and the second soft magnetic layer 114 c, acobalt-type alloy, such as CoTaZr; a Co—Fe-type alloy, such as CoCrFeB;a Ni—Fe-type alloy having a [Ni—Fe/Sn]n multilayered structure or thelike can be used.

The preliminary ground layer 116 is a non-magnetic alloy layer, andincludes an operation of protecting the soft magnetic layer 114 and afunction of orienting in a disk perpendicular direction an easy axis ofmagnetization of a hexagonal close-packed structure (hcp structure)included in the ground layer 118 formed on the preliminary ground layer.In the preliminary ground layer 116, a (111) surface of a face-centeredcubic structure (fcc structure) or a (110) surface of a body-centeredcubic structure (bcc structure) are preferably parallel to a mainsurface of the disk base 110. Also, the preliminary ground layer mayhave a structure in which these crystal structures and amorphous aremixed. As a material of the preliminary ground layer 116, a selectioncan be made from Ni, Cu, Pt, Pd, Zr, Hf, Nb, and Ta. Furthermore, analloy including any of these metals as a main element and any one ormore additional elements from among Ti, V, Ta, Cr, Mo, and W may beused. For example, NiW, CuW, or CuCr can be suitably selected as an fccstructure, and Ta can be suitably selected as a bcc structure.

The ground layer 118 has a hcp structure, and has an operation ofgrowing crystals of the hcp structure of the magnetic recording layer122 as a granular structure. Therefore, as the crystal orientation ofthe ground layer 118 is higher, that is, a (0001) surface of a crystalof the ground layer 118 is more parallel to the main surface of the diskbase 110, the orientation of the magnetic recording layer 122 can beimproved. As a material of the ground layer 118, Ru is typical. Otherthan that, a selection can be made from RuCr and RuCo. Ru has a hcpstructure, and a lattice space of the crystal is similar to that of Co.Therefore, the magnetic recording layer 122 having Co as a maincomponent can be oriented in good condition.

When the ground layer 118 is made of Ru, by changing the gas pressure atthe time of sputtering, a two-layer structure made of Ru can beachieved. Specifically, when the second ground layer 118 b on anupper-layer side is formed, the gas pressure of Ar is made higher thanthat when the first ground layer 118 a on a lower-layer side is formed.When the gas pressure is made higher, a free traveling distance of Ruions to be sputtered is shortened, and therefore the film-forming speedbecomes slow, thereby improving the crystal separation ability. Also,with a high pressure, the size of the crystal lattice becomes smaller.Since the size of the crystal lattice of Ru is larger than that of thecrystal lattice of Co, when the crystal lattice of Ru is made smaller,it becomes closer to that of Co, thereby further improving the crystalorientation of the Co granular layer.

The non-magnetic granular layer 120 is a non-magnetic granular layer. Byforming a non-magnetic granular layer on the hcp crystal structure ofthe ground layer 118 and, on that layer, making a granular layer of thefirst magnetic recording layer 122 a grown, an operation of separatingthe magnetic granular layer from a stage of initial growth (leading) isprovided. The composition of the non-magnetic granular layer 120 can bea granular structure by forming a grain boundary by causing segregationof non-magnetic substance between non-magnetic crystal grains made of aCo-type alloy. In particular, CoCr—SiO₂ and CoCrRu—SiO₂ can be suitablyused and, furthermore, in place of Ru, Rh (rhodium), Pd (palladium), Ag(silver), Os (osmium), Ir (iridium), and Au (gold) can also be used.Still further, the non-magnetic substance is a substance in which agrain boundary part can be formed around magnetic particles so that anexchange interaction operation between magnetic particles (magneticgrains) is suppressed or interrupted, and can be any as long as it is anon-magnetic substance that is not incorporated into cobalt (Co).Examples can include silicon oxide (SiOx), chrome (Cr), chrome oxide(CrO₂), titanium oxide (TiO₂), zircon oxide (ZrO₂), and tantalum oxide(Ta₂O₅).

The magnetic recording layer 122 is a ferromagnetic layer having agranular structure in a columnar shape in which a grain boundary isformed by causing segregation of a non-magnetic substance aroundmagnetic particles made of a hard magnetic body selected from a Co-typealloy, a Fe-type alloy, and a Ni-type alloy. By providing thenon-magnetic granular layer 120, these magnetic particles can make anepitaxial growth continuously from their granular structure. In thepresent embodiment, the magnetic recording layer is configured of thefirst magnetic recording layer 122 a and the second magnetic recordinglayer 122 b different in composition and film thickness. In both of thefirst magnetic recording layer 122 a and the second magnetic recordinglayer 122 b, as a non-magnetic substance, an oxide, such as SiO₂, Cr₂O₃,TiO₂, B₂O₃, and Fe₂O₃; a nitride, such as BN; or a carbide, such as B₄C₃can be suitably used.

In the present embodiment, A<B when an average particle diameter of themagnetic particles (crystal grains) in the first magnetic recordinglayer 122 a is taken as A nm and an average particle diameter of themagnetic particles (crystal grains) in the second magnetic recordinglayer 122 b is taken as B nm. With the particle diameter of the magneticparticles of the first magnetic recording layer 122 a being smaller thanthe particle diameter of the magnetic particles of the second magneticrecording layer 122 b, the magnetic particles can be made finer in thefirst magnetic recording layer 122 a, and the orientation of themagnetic particles can be improved in the second magnetic recordinglayer 122 b. Making the magnetic particles finer and improving theorientation have a trade-off relation. Therefore, with the abovestructure, the magnetic recording layers 122 can play the respectiveroles, and it is thus possible to improve the SNR while maintaining ahigh coercive force Hc.

Still further, in the present embodiment, in either one or both of thefirst magnetic recording layer 122 a and the second magnetic recordinglayer 122 b, two or more non-magnetic substances can be used in acompounding manner. Here, although the type of non-magnetic substancecontained is not restricted, SiO₂ and TiO₂ are in particular preferablyincluded and, next, in place of/in addition to either one, Cr₂O₃ can besuitably used. For example, the first magnetic recording layer 122 a cancontain Cr₂O₃ and SiO₂, as an example of the composite oxide (oxides ofa plurality of types), in a grain boundary part to form an hcp crystalstructure of CoCrPt—Cr₂O₃—SiO₂. Also, for example, the second magneticrecording layer 122 b can contain SiO₂ and TiO₂, as an example of thecomposite oxide, in a grain boundary part to form an hcp crystalstructure of CoCrPt—SiO₂—TiO₂.

The continuous layer 124 is a magnetically continuous layer (alsoreferred to as a continuous layer) in an in-plane direction on themagnetic recording layer 122 having a granular structure. Although thecontinuous layer 124 is not necessarily required, by providing this, inaddition to a high-density recording property and a low-noise propertyof the magnetic recording layer 122, it is possible to enhance theinverted-magnetic-domain nucleation magnetic field Hn, improve theheat-resistant fluctuation characteristic, and improve the overwritecharacteristic.

The medium protective layer 126 can be formed by forming a film out ofcarbon by CVD while keeping a vacuum state. The medium protective layer126 is a protective layer for protecting the perpendicular magneticrecording layer from a shock of the magnetic head. In general, a carbonfilm formed by CVD has an improved film hardness compared with the oneformed by sputtering, and therefore the perpendicular magnetic recordingmedium can be more effectively protected from a shock from the magnetichead.

The lubricating layer 128 can be formed by forming a film out ofperfluoropolyether (PFPE) by dip coating. PFPE has a molecular structurein a long chain shape, and is coupled to an N atom on the surface of themedium protective layer 126 with high affinity. With this operation ofthe lubricating layer 128, a damage or loss of the medium protectivelayer 126 can be prevented even if the magnetic head makes contact withthe surface of the perpendicular magnetic recording medium 100.

With the above manufacturing processes, the perpendicular magneticrecording medium 100 can be obtained. In the following, effectiveness ofthe present invention is described by using an example and comparativeexamples.

EXAMPLES AND EVALUATION

On the disk base 110, by using a vacuumed film forming device, theadhesion layer 112 to the continuous layer 124 were sequentially formedin an Ar atmosphere by DC magnetron sputtering. The adhesive layer 112was of CrTi. In the soft magnetic layer 114, the composition of thefirst soft magnetic layer 114 a and the second soft magnetic layer 114 cwas of FeCoTaZr, and the composition of the spacer layer 114 b was ofRu. The composition of the preliminary ground layer 116 was of an NiWalloy with an fcc structure. In the ground layer 118, the first groundlayer 118 a was formed out of Ru under low-pressure Ar, and the secondground layer 118 b was formed out of Ru under high-pressure Ar. Thecomposition of the non-magnetic granular layer 120 was of non-magneticCoCr—SiO₂. The magnetic recording layer 122 was formed with a structurein the example and comparative examples below. The composition of thecontinuous layer 124 was of CoCrPtB. As for the medium protective layer126, a film was formed by using C₂H₄ and CN by CVD, and the lubricatinglayer 128 was formed by using PFPE by dip coating.

FIG. 2 is a descriptive diagram for describing a relation between gaspressure and SNR and a relation between input power and SNR at the timeof forming the magnetic recording layer 122. In particular, FIG. 2( a)is a diagram showing a relation between a condition (gas pressure andinput power) for forming the second magnetic recording layer 122 b, andSNR, with a film thickness of the first magnetic recording layer 122 abeing fixed at 3 nm and an average particle diameter of the magneticparticles at 6 nm. FIG. 2( b) is a diagram showing a relation between acondition (gas pressure and input power) for forming the first magneticrecording layer 122 a, and SNR, with a film thickness of the secondmagnetic recording layer 122 b being fixed at 10 nm and an averageparticle diameter of the magnetic particles at 7 nm. Note that, ineither case, a film-forming time is adjusted so that the product of theinput power and the film-forming time is constant, thereby making thefilm thickness constant. In this case, in the first magnetic recordinglayer 122 a, an hcp crystal structure of CoCrPt—Cr₂O₃—SiO₂ was formed byincluding Cr₂O₃ and SiO₂ as an example of a composite oxide. Also, inthe second magnetic recording layer 122 b, an hcp crystal structure ofCoCrPt—SiO₂—TiO₂ was formed by including SiO₂ and TiO₂ as an example ofa composite oxide.

As depicted in FIG. 2( a), in the second magnetic recording layer 122 b,an optimum SNR can be obtained by forming a film at a gas pressure of2.5 Pa and an input power of 400 W. The average particle diameter of themagnetic particles of the second magnetic recording layer 122 b at thistime can be measured by a Transmission Electron Microscope (TEM), andthe results were such that the average particle diameter was 6.7 nm.

As depicted in FIG. 2( b), in the first magnetic recording layer 122 a,an optimum SNR can be obtained by forming a film at a gas pressure of3.0 Pa and an input power of 200 W. An average particle diameter ofmagnetic particles of the first magnetic recording layer 122 a at thistime can be measured by a transmission electron microscope, and was 6.5nm.

In the following, it is assumed as a first example that the firstmagnetic recording layer 122 a has an average particle diameter of themagnetic particles of 6 nm and the second magnetic recording layer 122 bhas an average particle diameter of the magnetic particles of 7 nm, thatis, the first magnetic recording layer 122 a<the second magneticrecording layer 122 b regarding the average particle diameter of themagnetic particles. Also, it is assumed as a comparative example thatthe first magnetic recording layer 122 a has an average particlediameter of the magnetic particles of 7 nm and the second magneticrecording layer 122 b has an average particle diameter of the magneticparticles of 6 nm, that is, the first magnetic recording layer 122 a>thesecond magnetic recording layer 122 b regarding the average particlediameter of the magnetic particles.

FIG. 3 is a descriptive diagram for describing a relation between anaverage particle diameter of magnetic particles of the first magneticrecording layer 122 a and an average particle diameter of magneticparticles of the second magnetic recording layer 122 b and an SNRrelation therebetween.

As depicted in FIG. 3, when the particle diameter of the magneticparticles included in the first magnetic recording layer 122 a issmaller than the particle diameter of the magnetic particles included inthe second magnetic recording layer 122 b, a high SNR can be obtained,compared with the case in which the particle diameter of the magneticparticles included in the first magnetic recording layer 122 a is largerthan the particle diameter of the magnetic particles included in thesecond magnetic recording layer 122 b.

Also, with the average particle diameter of the magnetic particles inthe first magnetic recording layer 122 a being smaller by approximately1 nm than the average particle diameter of the magnetic particles in thesecond magnetic recording layer 122 b (A/B≈(nearly equal)0.85 when theaverage particle diameter of the magnetic particles in the firstmagnetic recording layer 122 a is taken as A and the average particlediameter of the magnetic particles in the second magnetic recordinglayer 122 b is taken as B), the SNR can be optimally improved. Notethat, as depicted in the comparison example, if a ratio (A/B) betweenthe average particle diameter A of the magnetic particles in the firstmagnetic recording layer 122 a and the average particle diameter B ofthe magnetic particles in the second magnetic recording layer 122 b is1.16, that is, equal to or larger than 1, a role of making each magneticrecording layer 122 finer and a role of improving orientation cannot beshared, and therefore an improvement of the SNR cannot be expected evenif two magnetic recording layers 122 are provided.

With the aim of further improving the SNR, in a second embodiment, thefirst magnetic recording layer 122 a was configured to contain Cr₂O₃ andSiO₂ as an example of a composite oxide to form an hcp crystal structureof CoCrPt—Cr₂O₃—SiO₂, and the second magnetic recording layer 122 b wasconfigured to contain SiO₂ and TiO₂ as an example of a composite oxideto form an hcp crystal structure of CoCrPt—SiO₂—TiO₂.

As depicted in FIG. 3, with the second magnetic recording layer 122 bbeing formed so as to include a composite oxide of SiO₂ and TiO₂,characteristics of a plurality of oxides can be obtained. Therefore,noise was reduced by further making the magnetic grains of the magneticrecording layer 122 finer and more isolated, and also the SNR was ableto be improved.

In particular, SiO₂ has an effect of promoting finer and more isolatedmagnetic grains, and TiO₂ has an effect of suppressing dispersion inparticle diameter of the crystal grains. By combining these oxides forsegregation over the grain boundary parts of the magnetic recordinglayer 122, both of the advantages can be enjoyed.

FIG. 4 is a descriptive diagram for describing the perpendicularmagnetic recording medium 100 manufactured by using the method ofmanufacturing a perpendicular magnetic recording medium according to thepresent embodiment.

As depicted in FIG. 4, the perpendicular magnetic recording medium 100manufactured by using the method of manufacturing a perpendicularmagnetic recording medium according to the present embodiment is formedso that the average particle diameter of the magnetic particles (crystalgrains) in the first magnetic recording layer 122 a is smaller than theaverage particle diameter of the magnetic particles (crystal grains) inthe second magnetic recording layer 122 b. Therefore, the magneticparticles can be made finer in the first magnetic recording layer 122 a,and the orientation of the magnetic particles can be reliably controlledin the second magnetic recording layer 122 b. Making the magneticparticles finer and improving the orientation have a trade-off relation.Therefore, with the above structure, the magnetic recording layers 122can play the respective roles, and it is thus possible to improve theSNR while maintaining a high coercive force Hc.

Also, the present embodiment can be applied to the non-magnetic granularlayer 120. That is, with the average particle diameter of thenon-magnetic granular layer 120 being smaller than the average particlediameter of the first magnetic recording layer 122 a, the averageparticle diameter of the first magnetic recording layer 122 a can beeffectively reduced, and the magnitude relation between crystal grains(magnetic particles) of the first magnetic recording layer 122 a and thesecond magnetic recording layer 122 b can be adjusted.

Furthermore, in the above embodiments and examples, it is described thatthe magnetic recording layer 122 is formed of two layers, that is, thefirst magnetic recording layer 122 a and the second magnetic recordinglayer 122 b. However, even when the magnetic recording layer 122 isformed of three or more layers, an effect similar to the above can beachieved by at least setting the average particle diameter of themagnetic particles of an upper magnetic recording layer 122 as beinglarger than the average particle diameter of the magnetic particles of alower magnetic recording layer 122.

In the foregoing, the preferred examples of the present invention havebeen described with reference to the attached drawings. Needless to say,however, the present invention is not restricted by such examples. It isclear that the person skilled in the art can conceive variousmodification examples or corrected examples within a range described inthe scope of claims for patent, and it is understood that these examplesreasonably belong to the technological scope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention can be used as a perpendicular magnetic recordingmedium implemented on an HDD (hard disk drive) of a perpendicularmagnetic recording type or the like, and a method of manufacturing aperpendicular magnetic recording medium.

The invention claimed is:
 1. A method of manufacturing a perpendicularmagnetic recording medium including at least a ground layer, anon-magnetic granular layer, a first magnetic recording layer, and asecond magnetic recording layer in this order on a base, comprising:forming the first magnetic recording layer using a magnetic target thatincludes, in a composition, any of chrome, oxygen, or an oxide, or aplurality of oxides, and a gas pressure of approximately 0.5 Pa and apower of approximately 100 to approximately 700 W are set, therebyforming a ferromagnetic layer of a granular structure in whichnon-magnetic grain boundary parts are formed each between crystal grainseach grown in a columnar shape, forming the second magnetic recordinglayer using a magnetic target that includes, in a composition, any ofchrome, oxygen, or an oxide, or a plurality of oxides, and where a gaspressure of approximately 0.5 Pa and a power of approximately 100 toapproximately 1000 W are set, wherein the second magnetic recordinglayer is a ferromagnetic layer of a granular structure in whichnon-magnetic grain boundary parts are formed each between crystal grainseach grown in a columnar shape, and wherein A<B when an average particlediameter of the crystal grains in the first magnetic recording layer istaken as A nm and an average particle diameter of the crystal grains inthe second magnetic recording layer is taken as B nm, and the averageparticle diameter of the non-magnetic granular layer is smaller than theaverage particle diameter of the first magnetic recording layer.
 2. Themethod of manufacturing a perpendicular magnetic recording mediumaccording to claim 1, wherein a ratio between the average particlediameter of the crystal grains in the first magnetic recording layer andthe average particle diameter of the crystal grains in the secondmagnetic recording layer is 0.8<A/B<1.
 3. The method of manufacturing aperpendicular magnetic recording medium according to claim 1, wherein atotal thickness of the first magnetic recording layer and the secondmagnetic recording layer is equal to or smaller than 15 nm.
 4. Themethod of manufacturing a perpendicular magnetic recording mediumaccording to claim 1, wherein a non-magnetic substance in which a grainboundary part can be formed includes any of chrome, oxygen, or an oxide,or a plurality thereof.
 5. The method of manufacturing a perpendicularmagnetic recording medium according to claim 4, wherein the oxideincludes one or a plurality of oxides selected from the group of SiO₂,TiO₂, Cr₂O₃, Ta₂O₅, Nb₂O₅, B₂O₃, and ZrO₂.
 6. The method ofmanufacturing a perpendicular magnetic recording medium according toclaim 4, wherein an oxide included in the second magnetic recordinglayer includes one or a plurality of oxides selected from the group ofSiO₂, TiO₂, Cr₂O₃, Ta₂O₅, Nb₂O₅, B₂O₃, and ZrO₂.
 7. The method ofmanufacturing a perpendicular magnetic recording medium according toclaim 2, wherein a total thickness of the first magnetic recording layerand the second magnetic recording layer is equal to or smaller than 15nm.
 8. The method of manufacturing a perpendicular magnetic recordingmedium according to claim 2, wherein a non-magnetic substance in which agrain boundary part can be formed includes any of chrome, oxygen, or anoxide, or a plurality thereof.
 9. The method of manufacturing aperpendicular magnetic recording medium according to claim 3, wherein anon-magnetic substance in which a grain boundary part can be formedincludes any of chrome, oxygen, or an oxide, or a plurality thereof. 10.The method of manufacturing a perpendicular magnetic recording mediumaccording to claim 8 wherein the oxide includes one or a plurality ofoxides selected from the group of SiO₂, TiO₂, Cr₂O₃, Ta₂O₅, Nb₂O₅, B₂O₃,and ZrO₂.
 11. The method of manufacturing a perpendicular magneticrecording medium according to claim 9, wherein the oxide includes one ora plurality of oxides selected from the group of SiO₂, TiO₂, Cr₂O₃,Ta₂O₅, Nb₂O₅, B₂O₃, and ZrO₂.
 12. The method of manufacturing aperpendicular magnetic recording medium according to claim 8, wherein anoxide included in the second magnetic recording layer includes one or aplurality of oxides selected from the group of SiO₂, TiO₂, Cr₂O₃, Ta₂O₅,Nb₂O₅, B₂O₃, and ZrO₂.
 13. The method of manufacturing a perpendicularmagnetic recording medium according to claim 9, wherein an oxideincluded in the second magnetic recording layer includes one or aplurality of oxides selected from the group of SiO₂, TiO₂, Cr₂O₃, Ta₂O₅,Nb₂O₅, B₂O₃, and ZrO₂.
 14. The method of manufacturing a perpendicularmagnetic recording medium according to claim 1 wherein the non-magneticgranular layer includes non-magnetic crystal grains made of a Co alloyand a grain boundary part that comprises at least one of SiOx, Cr, CrO₂,TiO₂, ZrO₂ and Ta₂O₅.
 15. A method of manufacturing a perpendicularmagnetic recording medium including at least a ground layer, a firstmagnetic recording layer, a second magnetic recording layer, and atleast a third magnetic recording layer, said layers being provided inthis order on a base, comprising: forming the first magnetic recordinglayer, the second magnetic recording layer and the at least a thirdmagnetic recording layer as ferromagnetic layers of a granular structurein which grain boundary parts made of a non-magnetic substance are eachformed between crystal grains each grown in a columnar shape, and theaverage particle diameter of the magnetic particles of an upper magneticrecording layer selected from the at least one third magnetic layer,relative to the base side is larger than the average particle diameterof the magnetic particles of a lower magnetic recording layer selectedfrom only one but not the other of the first and second magnetic layers,relative to the upper magnetic recording layer.
 16. A method ofmanufacturing a perpendicular magnetic recording medium including atleast a ground layer, a first magnetic recording layer, a secondmagnetic recording layer, and at least a third magnetic recording layer,said layers being provided in this order on a base, comprising: formingthe first magnetic recording layer, the second magnetic recording layerand the at least a third magnetic recording layer as ferromagneticlayers of a granular structure in which grain boundary parts made of anon-magnetic substance are each formed between crystal grains each grownin a columnar shape, wherein A<B when an average particle diameter ofthe crystal grains in the first magnetic recording layer is taken as Anm and an average particle diameter of the crystal grains in the secondmagnetic recording layer is taken as B nm, and wherein the averageparticle diameter of the magnetic particles of an upper magneticrecording layer selected from the second and third magnetic layers,relative to the base side is larger than the average particle diameterof the magnetic particles of a lower magnetic recording layer selectedfrom the first and second magnetic layers, relative to the uppermagnetic recording layer, and forming a non-magnetic granular layerbetween the ground layer and the first magnetic recording layer, thenon-magnetic granular layer having an average particle diameter smallerthan the average particle diameter of the first magnetic recordinglayer.
 17. The method according to claim 16 wherein the non-magneticgranular layer includes non-magnetic crystal grains made of a Co alloyand a grain boundary part that comprises at least one of SiOx, Cr, CrO₂,TiO₂, ZrO₂ and Ta₂O₅.
 18. The method according to claim 17 wherein thenon-magnetic granular layer comprises Co, Cr, SiO₂ and at least one ofRu, Rh, Pd, Ag, Os, Ir and Au.